On-load tap changers (in abbreviation OLTC) are widely known and conventional in the prior art. They serve for uninterrupted changeover between different winding taps of tapped transformers.
Such on-load tap changers are divided into load selectors and load changeover switches with selectors.
In a load-changeover switch with a selector such as disclosed in, for example, German Patent Specification DE 100 55 406 the selector, which consists of a fine selector and possibly a preselector, is below the load changeover switch. The selector serves for power-free selection of the respective new winding tap to be switched over to, of the tapped transformer. The load changeover switch serves for the subsequent rapid and uninterrupted changeover from the connected to the new, preselected winding tap to be connected.
Load selectors such as described in, for example, German Patent Specification DE 28 33 126 serve, just like the load changeover switch with a selector, the purpose of switching over the taps of the regulating windings of these tapped transformers under load and thus of providing selective compensation for voltage changes at the user. Through dispensing with the separation of the load changeover switch from selector, load selectors can be produced at lower cost. Load selectors have only a limited range of use, such as, for example, due to the limited possible number of taps.
Both kinds of on-load tap changers are actuated by a motor drive for the changeover process. A drive output or drive input shaft, which loads a force-storing unit, is moved by the motor drive. When the force-storing unit is completely loaded, i.e. stressed, it is unlatched, abruptly releases its energy and actuates a load changeover switch insert in a space of milliseconds (ms) that in that case executes a specific switching sequence during the load changeover. Different switch contacts and resistance contacts are then actuated in a specific sequence in time. The switch contacts in that case serve for direct connection of the respective winding tap with the load diverter and the resistance contacts serve for temporary connection, i.e. bridging-over by one or more switching-over resistances. Advantageously, vacuum interrupters are used as switch elements for the load changeover. This is based on the fact that the use of vacuum interrupters for the load changeover prevents formation of arcs in the oil and thus oil contamination of the load changeover switch oil, such as described in, for example, German Patent Specifications DE 195 10 809 [U.S. Pat. No. 5,834,717] and DE 40 11 019 [U.S. Pat. No. 5,107,200] as well as German published specifications DE 42 31 353 and DE 10 2007 004 530 A1.
The centrally rotating transmission and the actuators as well as the stationary contact and resistor subassemblies are disadvantageous with these on-load tap changers. This is due to the fact that, for example, complex support elements are necessary for the switching segments or also the resistor subassembly and these elements have to be differently arranged in the load selector. Moreover, flexible contact or current connections are needed. Added to that is the fact that some components have to be produced precisely and free of distortion in such a way that they can be installed in the on-load tap changer. If these components were to be produced by an injection-molding process, an individual injection-molding tool would have to be made for each of the different components that increases the costs of an on-load tap changer.
Thus, German specification DE 1 231 805 B already discloses a tap selector for tap changers of regulating transformers preferably below a load changeover switch and is constructed in accordance with a modular principle so that the tap selector is capable of use for different tap changers.
The object of the invention is to create a simple and economic on-load tap changer that uses a large number of identical parts with respect to load selector or load changeover switch so that different functionalities of the on-load tap changer can be realized.